The present invention relates to saw chains for chain saws and, in particular, to a configuration of side links of the saw chain.
As depicted in FIG. 4, a saw chain 2 for cutting wood is usually made with center drive links 4, and side links 6. The purpose of the drive links 4 is to drive the chain in direction D by a force from a motor-powered drive sprocket (not shown) and to guide the chain along a groove around the edge of a guide bar (not shown). The side links 6 are connected to the drive links for the purpose of carrying loads in the plane of the guide bar by sliding contact with the guide bar edge rails on each side of the groove. Some of the side links 6A may serve as cutter links.
To minimize wear of the side links a lubricant is fed to the groove by a pump, and distributed along the groove by a scoop-like cutout in the lower part of the center links. The lubricant will spread to the inner sides of the groove to lubricate the sides of the drive links, although only small forces act between the link sides and the groove sides. The lubricant will also spread upwards along the center links to lubricate the rivets connecting the drive links to the side links. Some lubricant will also spread to the edge rails, where it is needed because there is always sliding friction with considerable pressure between the chain and the rails due to the curvature and the cutting force.
Most guide bars have today a nose sprocket to carry a curved front portion of the chain around the guide bar nose without imposing a radial load on the side links, leaving the straight cutting portion of the chain as the most critical region for lubrication. Unfortunately this portion is also the most inaccessible, since the chain has by then already travelled the length of the guide bar, as well as around the nose with extreme rotational velocity, and thrown off most of the lubricant. Various guide bar designs have been suggested with lubricant channels extending to or past the nose, such as U.S. Pat. No. 2,748,810.
A further complicating factor is that the lower contact surface of a side link is usually provided with two heels located at respective front and rear ends of the link. The heels are oriented for sliding contact along the longitudinal edges of the guide bar, which edges are not straight in cross section but instead are slightly convex to ensure that tension in the chain will keep the chain in the groove even when it is not cutting. The heels are thus flat bottomed and almost, but not quite, aligned with one another. Between the heels the link may have a cutout with a large radius to fit the guide bar nose if the chain is to be used on a guide bar without nose sprocket, or with a sprocket lifting the links only a small distance off the edges. In the middle there is often a deeper cutout to allow higher teeth to be used on the nose sprocket.
If the heels of the side link are made to fit the edge rails with a fairly large contact surface but have an abrupt front end, most of the lubricant will be pushed off the edge rail with no beneficial effect on the wear. There has been a number of suggestions for heel designs where the lubricant is supposed to be retained on the edge rail to minimize wear. Ehlen et al. U.S. Pat. No. 3,170,497 shows in front of the front heel an extension with an inclined bottom, creating a wedge-shaped space to squeeze the lubricant under the heel. Dolata et al. U.S. Pat. No. 3,921,490 shows that the front heel can be shortened to make room for the inclined bottom without an extension. Neither of these expedients is very effective, since most of the lubricant is squeezed out to the side rather than under the heel.
The present invention concerns a saw chain with side links designed to collect and concentrate the lubricant onto the edge rails and to act as hydrodynamic bearings sliding along the edge rails without metallic contact.